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VOLTAGE SELECTION IN SAME CON SWITCH SELECTABLE D.C. PITCH POTENTIAL AN CONSTANT A.C. FOR CONTROL FUNCTION Filed A ril 10, 19s? 4 Sheets-Sheet 2 I/VI/E/VTOR. ALFRED L. MALLEIT May 12, 1970 A. MALLETT 3,5 ,9 A VOLTAGE SELECTION ARRANGEMENT WHEREIN SAME CONTACTS v SWITCH SELECTABLE D.C. PITCH POTENTIAL AND CONSTANT A-C. FOR CONTROL FUNCTION 4 Sheets-Sheet 3 Filed April 10. 1967 INVENTOR. ALFRED L. MALL E77 El is- May 12, 1970 I A. L. MALLETT 3,511,917 VOLTAGE SELECTION ARRANGEMENT WHEREIN SAME CONTACTS SWITCH SELECTABLE D.C. PITCH POTENTIAL AND CONSTANT A-C. FOR CONTROL FUNCTION Filed April 10, 1967 4 Sheets-Sheet 4.

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ALFRED L. MALLETT United States Patent 3,511,917 VOLTAGE SELECTION ARRANGEMENT WHERE- IN SAME CONTACTS SWITCH SELECTABLE D.C. PITCH POTENTIAL AND CONSTANT A.C. FOR CONTROL FUNCTION Alfred L. Mallett, Pittslield, N.H., assignor to The Seeburg Corporation of Delaware, Chicago, Ill., a corporation of Delaware Filed Apr. 10, 1967, Ser. No. 629,560 Int. Cl. G10h /06, 1/02; H03k 5/20 US. Cl. 841.01 13 Claims ABSTRACT OF THE DISCLOSURE An apparatus having single-pole, double-throw switches which provide selection at will of one of a plurality of discrete DC voltages with an AC signal superimposed thereon. The DC voltage with superimposed AC signal is conveyed to a biased diode network that filters out the AC signal and passes the discrete DC voltage to a storage circuit to perform a control function. Simultaneously, the DC voltage with superimposed AC signal is conveyed to another circuit which filters out the DC voltage and converts the AC signal to a given magnitude DC reference voltage to perform other control functions.

BACKGROUND OF THE INVENTION :Field of the invention This invention relates generally to an arrangement for selecting a particular voltage from a plurality of discrete voltages, and more particularly this invention relates to an arrangement for selecting a discrete voltage from a plurality of discrete voltages each of which represents a note of a musical instrument, such as an electronic organ. I

Description of the prior art In the electronic musical instrument art, with particular emphasis on the electronic organ art, it is necessary to produce tone signals representative of the notes of the chromatic scale. In an electronic organ a particular tone signal is selected by actuation of a pedal in an organ pedal keyboard that corresponds to that note. One method of achieving production of the desired tone signals is to provide an individual tone generator for each tone signal, each of the tone generators being tuned to the frequency of a note represented by a corresponding pedal. In such an arrangement each pedal controls the actuation of an individual switch between the corresponding tone generator and an audio output circuit. Also, each of the individual switches is ganged with a common switch in a circuit that produces a DC voltage having a given magnitude. Actuation of any of the pedals closes the common switch so that the DC voltage is applied to an appropriate keying circuit to regulate the tone signal output. This arrangement, of course, is bulky and expensive due to the use of extensive circuitry and a multiplicity of relatively expensive tone generators.

A generally more desirable approach is to utilize a single, variable-frequency, voltage-responsive tone generator. By determining the characteristics of the variable frequency tone generator, it is possible to calculate the required magnitude of control voltage that needs to be applied to the tone generator in order to obtain a specified frequency. The dilferent magnitude control voltages to be applied to the tone generator may be obtained by utilizing a DC voltage divider having a plurality of taps at positions corresponding to the desired magnitude control voltages. In order to provide a multiplicity of control voltages to the variable-frequency oscillator and a constant ice magnitude voltage for other functions, such as keying, a switch for each of the control voltages is ganged with a switch for the constant voltage. Alternatively double-pole, double-throw switches may be used, with one pole controlling application of the variable voltages and the other pole controlling application of the constant magnitude voltage. Such switching arrangements cause many problems due to mechanical inaccuracies. For instance, in the case of both ganged switches and double-pole, double-throw switches the switches tend to become missynchronized, thereby causing many problems in musical instruments which depend upon accurate synchronization of the control functions to produce desired musical renditions.

It is well known that single-pole switches are more reliable than ganged or double-pole switches and do not require as much periodic adjustment. Thus, by substituting single-pole switches for ganged or double-pole switches many of the problems associated with prior art arrangements may be eliminated. However, in order to use single-pole switches with a musical instrument such as an electronic organ, it is necessary that actuation of any of the single-pole switches simultaneously provides a variable level .DC voltage to control a variable frequency oscillator and a DC reference signal of a given magnitude to perform ancillary functions.

Another problem is presented by the fact that in many instances an electronic musical instrument must yield more than one octave of musical notes. One way to achieve such a multiple octave instrument is to increase the frequency range of the variable frequency oscillator to include the additional octaves, but this results in frequency instability of the oscillator and requires highly accurate values for the discrete control voltages. To avoid the problems inherent in a variable frequency oscillator that covers multiple octave ranges it.is possible to have the oscillator variable cover a single octave and provide for frequency division of the oscillator output signal.

One method of achieving frequency division is to have the output of the oscillator conveyed to a series of frequency divider circuits. However, this approach diminishes the magnitude of the resultant tone signals and tends to introduce undesirable sign-a1 distortion and loss of tone quality. A more desirable system is one utilizing a single frequency divider which may be regulated to yield the desired factor of division. Thus, the switching arrangement must also provide control of the frequency divider for the oscillator output signal, i.e., provide yet additional control signals, each having two separate magnitudes and each being related to one range of the discrete control voltages. In the case of an electronic musical instrument these additional control signals would each be associated with a range of discrete voltages corresponding to one octave of notes.

SUMMARY OF THE INVENTION Briefly, in the preferred embodiments disclosed herein, discrete DC voltages each corresponding to a musical instrument (such as an organ) note have an AC signal superimposed thereon. The discrete DC voltages are obtained by connecting a constant value DC source across a resistive voltage divider network and tapping the voltage divider network at appropriate points. As it is desired to have the same magnitude AC signal superimposed on each discrete DC voltage, one side of :an AC supply is connected to each end of the voltage divider network. A switching arrangement comprising a plurality of singlepole, double-throw switches is adapted to selectively connect the discrete DC voltages with the AC signal superimposed thereon to a detection circuit. Each switch, in an electronic organ, is actuated by an associated organ pedal corresponding to a particular musical note.

The detection circuit comprises a biased diode network including four diodes arranged as two pairs of seriesconnected diodes. One pairof diodes is normally biased in the forward direction and the voltage drop across each of these diodes is sufiicient to back-bias the diodes in the second pair. A storage capacitor is connected to ground from the common juncture of the diodes in the second pair of diodes. Discrete DC voltages with the AC signal superimposed thereon are conveyed from the switching arrangement to the common juncture of the diodes in the first pair of diodes. When-the switching arrangement is actuated (such as by the depression of a pedal of an electronic organ), a discrete DC voltag with the AC signal superimposed thereon is applied to the detection circuit,

which removes the AC signal and charges the storage capacitor to the level of the discrete DC voltage. The voltage on the storage capacitor is then applied to a voltage responsive circuit (such as a voltage dependent oscillator or tone generator in an electronic organ).

Besides applying a discrete DC voltage to a voltage responsive circuit, it is necessary to simultaneously provide other functions (e.g., in the organ a sustain keying function must be achieved). To achieve these additional functions the AC signal superimposed on the discrete DC voltages is separated from the discrete DC voltages and converted to a DC reference signal by a conversion circuit. Since the AC signal impressed on the discrete DC voltages has the same magnitude for all discrete DC voltages, the DC reference signal at the output of the conversion ciriuit has the same magnitude during each actuation of the switching arrangement. The resultant DC reference signal is then connected to an appropriate ancillary control circuit (such as a sustain keying circuit in an electronic organ).

In addition to providing an arrangement for achieving dual functions while using only single-pole switches, it is possible to modify the arrangement in order to achieve multiple functions. For example, in an electronic Organ additional pluralities of switches may be connected in series with the first plurality of switches, so that the discrete DC voltages with impressed AC signals therefrom are conveyed to respective additional conversion circuits 'to control octave division for a multiple octave tone generator. This is achieved by having the signals from each plurality of switches conveyed to the associated additional conversion circuit as well as the first conversion circuit, so that actuation of a switch in that plurality of switches energies the associated conversion circuit. Energization of one of the additional conversion circuits activates a corresponding flip-flop circuit that in turn controls the degree of frequency division practiced upon the output signal of the oscillator. Such frequency division permits the production of multiple octave tones without extending the frequency range of the oscillator beyond a single octave and without using a series of frequency dividers.

Accordingly, a primary object of this invention is to provide an arrangement for selecting one of a plurality of discrete DC voltages and for simultaneously conveying a DC reference signal of a given magnitude to an ancillary control circuit.

Another object of this invention is to provide an arrangement in which only one single-pole switch is used for simultaneously applying a discrete DC voltage to a 4 selection and ancillary circuit control may be achieved simultaneously by the use of single-pole switches.

Still another object of this invention is to provide an electronic organ tone selection arrangement that utilizes single-pole switches (l) to achieve tone selection, (2) to control produtcion of a keying voltage, and (3) to regulate frequency division of a single octave tone generator output to provide multiple octave tones.

These and other objects, advantages, and features of the subject invention will hereinafter appear and, for purposes of illustration, but not of limitation, exemplary embodiments of the subject invention are shown in the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING 7 FIG. 1 is a schematic block diagram of an electronic organ tone selection and generating arrangement illustrating a preferred embodiment of the present invention.

FIG. 2 is a detailed schematic circuit diagram of a first portion of the arrangement illustrated in FIG. 1.

FIG. 3 is a detailed schematic circuit diagram of a second portion of the arrangement illustrated in FIG. 1.

FIG. 4 is a schematic diagram illustrating the relationship between FIGS. 2 and 3.

FIG. 5 is a schematic circuit diagram of a flip-flop circuit utilized in the FIG. 1 embodiment.

FIG. 6 is a partial schematic circuit diagram of another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the block diagram of FIG. 1, an electronic organ tone selection and generating circuit utilizing the subject invention is illustrated. While the electronic organ tone selection and generating circuit is one advantageous environment for this invention, it should be realized that the invention is not limited thereto.

In this preferred embodiment a voltage divider network 11 is utilized. A DC voltage source 13- is connected across the voltage divider network 11. Voltage divider network 11 and DC voltage source 13 together comprise a source of discrete DC voltages. An AC supply 15 has one side thereof connected to each end of voltage divider network 11 via coupling capacitors 17 and 19. Capacitors 17 and 19 couple the AC signal from the AC supply 15 to the voltage divider network 11 and bar the passage of DC current from source 13 to AC supply 15. Capacitors 17 and 19' also serve to'prevent source 13 from being shorted out by the connections from the AC supply 15. The connection of AC supply 15 to the voltage divider network 11 in this fashion causes an AC signal of constant magnitude to be superimposed on each discrete DC voltage obtained from the voltage divider network 11.

Selection of a particular one of the discrete DC voltages on voltage divider network 11 is performed by switching circuit 21, which conveys the selected discrete DC voltage to a switching circuit output terminal 22. Control of switching circuit 21 may be achieved in any desired manner, but in the electronic organ this control is achieved by the pedals of the organ. A discrete DC voltage with the AC signal superimposed thereon, as selected by switching circuit 21, is connected to detection circuit 23 through lead 25. The output of switching circuit 21 is also connected to a conversion circuit 27 through a coupling capacitor 29.

Detection circuit 23 removes the superimposed AC signal from the selected discrete DC voltage and charges a'storage capacitor.31 to the level of the discrete DC voltage. The DC voltage on capacitor 31 is passed through a unity gain DC amplifier 33, which includes a feedback resistor 35, and which serves toisolate capacitor 31 from the rest of the circuit. The DC voltage passed through unity gain amplifier 33 is then applied to a voltage controlled variable frequency oscillator 37. Voltage controlled oscillator 37 produces a tone signal having a frequency dependent upon the level of the voltage stored on storage capacitor 31.

The controlled frequency output of voltage controlled oscillator 37 is connected to a first flip-flop circuit 39. One output of flip-flop circuit 39 is applied to a second flip-flop circuit 41, and another output of flip-flop circuit 39 is conveyed to a keying circuit 43. An output signal from flip-flop circuit 41 is also applied to keying circuit 43.

Conversion circuit 27 converts the AC signal superimposed upon the discrete DC signal that passes through capacitor 29 to a DC reference signal. Since the AC signal superimposed on the discrete DC voltages is the same for every discrete DC voltage, the magnitude of the DC reference signal produced by conversion circuit 27 has a given magnitude. The DC reference signal produced by conversion circuit 27 is utilized as an ancillary circuit control signal. A primary function performed by the DC reference signal is that of actuating keying circuit 43. As long as keying circuit 43 is actuated by the DC reference signal from conversion circuit 27 the output of flip-flop circuit 39 will appear on the output terminal 45, and the output signal from flip-flop circuit 41 will appear on the output terminal 47. The signals appearing on the output terminals 45 and 47 have frequencies related by a factor of two. Thus, in the organ these signals would correspond to the octavely related signals appearing on the eight foot and sixteen foot bus bars. The duration of time for which keying circuit 43 is actuated by the DC reference signal after switching circuit 21 has been actuated is determined by a sustain circuit 49.

The DC reference signal produced by conversion circuit 27 may also be used for other control purposes. For instance, the leading edge of the DC reference signal may be converted to a pulse by a rhythm trigger circuit 51 for a rhythm control or rhythm indication function. This type of use is especially pertinent to an electronic organ incorporating an accompaniment or side man feature with an adjustable rhythm. The adjustable rhythm may be controlled by the pulses from rhythm trigger circuit 51 to .permit the accompanying rhythm orchestration to follow the rhythm at which the organ is being played.

The arrangement illustrated in block diagram form in FIG. 1 is shown in more detail in the circuit diagrams of FIGS. 2 and 3. In FIG. 3, a positive potential of 15 volts from DC source 13 is connected to the terminal 53. The other side of source 13 is connected to ground. The positive potential on terminal 53 is connected to a portion of the circuit shown in FIG. 2 via line 55. The 15 volt potential on line 55 is also connected to portions of the circuit shown in FIG. 3 by a line 57. From line 57 the positive voltage is connected through a variable resistor 59, a lead 61, and a fixed resistor 63 to a terminal 65 in the voltage divider network 11. Terminal 65 is also the midpoint of a voltage divider comprising resistors 67 and 69 connected between line 55 and ground. Another voltage divider comprising resistors 71 and 73 is connected from line 55. to ground. The midpoint 75 of this voltage divider is connected to a terminal 77 in the voltage divider network 11. Terminal 77 is also connected to ground through a fixed resistor 79 and a variable resistor 81.

Voltage divider network 11 comp-rises a series of twelve equal resistive elements 83. Between each pair of restrictive elements 83 are located tap points 85. There are eleven taps 85, and these taps, along with terminals 65 and 77, provide a total of thirteen equally separated discrete DC voltages representing the thirteen notes of the chromatic musical scale. By making resistor 67 equal to resistor 73 and resistor 69 equal to resistor 71, the voltage across the voltage divider network 11 (i.e., the voltage drop between terminal 65 and terminal 77) remains at a fixed value.

The variable resistor 59 may be adjusted to tune the organ so that the voltage appearing at terminal accurately represents high C on the chromatic scale. Similarly, variable resistor 81 may be set to tune the arrangement so that the voltage at terminal 77 accurately represents low C on the musical scale. However, even as resistors 59 and 81 are varied to change the voltages at terminals 65 and 77, the aforementioned relationship of resistors 67, 69, 71 and 73 maintains the total voltage drop between the terminals 65 and 77 at a fixed value. Thus, while the voltages at terminals 65 and 77 may be raised or lowered the voltage drop across each resistive element 83 is invariable. This guarantees that once the arrangement has been properly tuned for high C and low C the remaining notes of the scale are properly represented by the voltages appearing on taps 85.

An AC signal is obtained from the AC supply .15 illustrated in FIG. 2. AC supply 15 may be any conventional type of oscillator and may provide any of a wide range of frequencies. However, in the preferred embodiment disclosed herein, a solid state multivibrator oscillator tuned to a frequency of approximately twenty kilocycles has been utilized. This oscillator comprises a pair of transistors 87 and 89. Transistor 87 has an emitter 91, a base 93, and a collector 95, while transistor 89 has an emitter 97, a base 99, and a collector 101. The positive DC voltage from line 55 is connected to the oscillator circuit through a resistor 103. The potential obtained via resistor 103 is applied to a capacitor 105 which maintains the voltage at terminal 107 at a constant potential by smoothing out any variations that might occur. The potential at terminal 107 is connected to collector 95 of transistor 87 via a resistor 109, and to the collector .101 of transistor 89 through a resistor 111. The potential at terminal 107 is also connected to base 93 of transistor 87 through a resistor 113 and a diode 115. Similarly, base 99 of transistor 89 is connected to terminal 107 through a resistor 117 and a diode 119. Collector 95 of transistor 87 is connected to the juncture 121 of resistor 117 and diode 119 by a capacitor 123. Similarly, collector 101 of transistor 89 is connected to the juncture 125 of resistor 113 and diode .115 by a capacitor 127. Resistors 109 and 111 are of the same magnitude, as are resistors 113 and v117 which have a magnitude large in comparison to that of resistors 109 and 111.

In operation, the oscillator of AC supply 15 will have an inherent imbalance causing one or the other of transistors 87 and 89 to begin conducting. For example it will be assumed that transistor 89 is initially conducting. As transistor 89 conducts a small base current will flow through resistor 117 and diode 1.19, which will cause capacitor 123 to charge to the magnitude of the drop across resistor 117. As transistor 89 is conducting the collector 101 will be essentially at ground potential, thereby causing capacitor 127 to begin charging through resistor 1.13. As capacitor 127 charges, the potential at point 125 will eventually become great enough to initiate conduction in transistor 87. As transistor 87 begins conduction collector 95 will approach ground potential and capacitor 123 will attempt to charge in the opposite direction to that in which it has been charging during conduction of transistor 89. This removes the current to base 99 of transistor 89, thereby tending to shut off transistor 89. As transistor 89 tends to cease conduction the potential in collector 101 rises above ground potential and capacitor 127 discharges through diode and the base-emitter junction of transistor 87. This discharge of capacitor 127 ensures full connection of transistor 87 at the same time that the current flow through resistor 1.11 is diverted to the path containing capacitor 127 and thereby furthers cut-off of transistor 89. This procedure is then repeated to produce a continuously oscillating condition in the multivibrator circuit.

The output of the multivibrator oscillator is taken from collector 101 of transistor 89 through resistor 129. The

output of AC supply circuit 15 is then connected to terminal 65 through capacitor 17 and to terminal 77 through capacitor 19. In this manner, the AC signal from the AC supply 15 is connected to both ends of the voltage divider network 11 and an AC signal having a constant magnitude is superimposed on each of the discrete DC voltages appearing at taps 85.

The discrete DC voltages appearing on taps 85 are selectively chosen by a switching arrangement 21. Switching arrangement 21 comprises a series of single-pole double-throw switches S-1 to S-13. Each of the switches has a movable contacting element 131, a stationary contact 133, and a stationary contact 135. Stationary contacts 135 are each connected to a respective tap 85.

Stationary contacts 133 are each connected to the movable contact 131 of a preceding switch in the series of switches from S-l to S-13. Movable contacts 131 are normally biased to contact stationary contacts 133. In this manner the switches -1 to S-13 are normally series connected to form a ladder arrangement.

The movable contact 131 of switch S-13 is connected to output terminal 22. Actuation of any of the switches S-1 to S-13 causes its associated movable contact 131 to be transferred from the stationary contact 133 to the stationary contact 135. Since each of the stationary contacts 135 is connected to a corresponding tap 85 in the voltage divider network 11, actuation of any of the switches S-1 to S13 causes a corresponding voltage to appear on terminal 22.

The thirteen switches S-1 to 5-13 correspond to the thirteen notes of the chromatic scale, in the same man ner as the thirteen voltages at terminal 65, taps 85 and terminal 77 correspond to these notes. When one of the switches S-1 to 5-13 is actuated, the discrete DC voltage corresponding to a particular note of the chromatic scale is connected to terminal 22. However, for actuation of a switch to produce this result each of the higher numbered switches (i.e., in the case of switch S-2 all of the switches S-3 to S-13) must be in the inactivated position (i.e., with movable contact 131 abutting stationary contact 133). With this arrangement, if two switches are simultaneously actuated only the higher numbered switch (corresponding to the lower note) will be effective to connect a voltage to terminal 22. Thus, the actuation of two switches simultaneously, which might otherwise produce a discordant sound, instead produces only the lower note corresponding to the higher numbered switch. The voltage appearing at terminal 22 is conveyed on two separate paths represented by lines 139 and 141. The signal conveyed on line 139 is applied to detection circuit 23. A capacitor 143 is connected from line 139 to ground in order to stabilize the DC voltage connected to detection circuit 23 and by-pass any high frequency signals to ground.

Detection circuit 23 comprises a first pair of diodes 145 and 147 and a second pair of very low reverse leakage diodes 149 and 151. Line 139 is connected to the common juncture 153 of diodes 145 and 147, while storage capacitor 31 is connected to ground from the common juncture of diodes 149 and 151. A resistor 157 is connected from the positive DC voltage on line 57 to a point between diodes 1-45 and 149. Similarly, a resistor 159 is connected from a point between diodes 147 and 151 to ground.

Detection circuit 23 removes the superimposed AC signal from the individually selected discrete DC voltages and charges capacitor 31 to the level of the selected discrete DC voltage. Normally, a current flow is produced through resistor 157, diode 145, diode 147, and through resistor 159 to ground. This current flow and the resulting voltage drops across diodes 145 and 147, along with the charge on capacitor 31, is sufficient to backbias diodes 149 and 151. However, when a discrete DC voltage with the AC signal superimposed thereon is connected to detection network 23, capacitor 31 will be charged through diodes 147 and 151 for a portion of the positive half cycle of the AC signal. For a portion of the negative half cycle of the AC signal capacitor 31 will be discharged through diodes and 149. If the discrete DC voltage appearing on line 139 is ditferent than the voltage to which capacitor 31 has been charged, the charging and discharging rates are unequal until the charge on capacitor 31 is the same as the discrete DC voltage on line 139. Thus, the detection circuit 23 strips the superimposed AC signal from the discrete DC voltage and charges capacitor 31 to the level of the discrete DC voltage appearing on line 139.

The biasing arrangement for diodes 145 and 147 is fixed by the resistive feedback 35 from the output of the unit gain amplifier 33. The output of the unit gain amplifier is essentially the same as the charge on capacitor 31, so that the juncture 153 of diodes 145 and 147 is at the same voltage level as the upper plate of capacitor 31. Due to the current flow through resistor 157, diode 145, diode 147, and resistor 159, there are slight voltage drops across diodes 145 and 147. Thus, the voltage on the cathode of diode 149 is slightly more positive than the voltage on capacitor 31 (which is the same voltage that appears at juncture point 153), and the voltage on the anode of diode 151 is slightly lower than the voltage on capacitor 31. This causes diodes 149 and 151 to be normaly backbiased.

Unity gain amplifier 33 is connected to the juncture 155 of diodes 149 and 151 and includes transistors 161, 163, 165, and 167. Collector 1 60 of transistor 161 is connected to the positive voltage on line 57 through resistor 169, while base 162 is connected to the juncture 155 of diodes 149 and 151. A capacitor 171 is connected across the emitter-collector circuit of transistor 161. Emitter 164 of transistor 163 and base 166 of transistor 167 are joined together and connected to base 168 of transistor through a resistor 173. Emitter 170 of transistor 165 is connected to a line through resistor 177. Line 175 is connected through a resistor 179 to a terminal 181 to which a negative DC potential of 25 volts is connected. A smoothing capacitor 183 is connected between line 175 and ground. Base 168 of transistor 165 is connected to one side of a capacitor 185, the other side of which is connected to ground.

The unity gain amplifier 33 serves as an isolation amplifier for capacitor 31 and is connected as a Darlington amplifier. This arrangement provides a high input impedance for isolating capacitor 31 and a low output impedance for driving the successive portions of the circuit.

In operation, the unity gain amplifier 33 is dependent upon the charge existing on capacitor 31. The voltage on capacitor 31 is applied to base 162 of transistor 161 to control the conduction of that transistor. The rate of conduction of transistor 161 controls the rate of conduction of transistor 163. As transistor 163 conducts the potential on the base 166 of transistor 167 varies to control the conduction of that transistor and hence the charging of capacitor 185 through transistor 167. If the charge on capacitor 185 exceeds the value of the charge on capacitor 31 transistor 165 isbiased to a conducting state, since the potential on the emitter of transistor 161, and hence on the emitter of transistor 165, is essentially the voltage impressed on capacitor 31. Conduction of transistor 165 increases the current flow through resistor 177 and thereby raises the poential at the emitter of transistor 161. This reduces the conduction of transistor 161, reduces the conduction of transistor 163, which reduces the conduction of transistor 1 67 and hence reduces the charging rate of capacitor 185. In this manner, the voltage impressed across capacitor 185 is held to the value of voltage impressed across capacitor 31. Thus, the capacitor 31 is isolated from the rest of the circuit and yet the voltage to which it is changed is still available acrosscapacitor 185 to control the oscillator 37.

The voltage appearing across capacitor 185 is connected to the emitter 187 of a transistor 189 through a resistor 191. Transistor 189 also has a base 193 and a collector 195. Collector 195 of transistor 189 is connected to line 175 through a capacitor 197. Resistor 191 and capacitor 197 serve as the normal charging circuit for a conventional unijunction transistor oscillator (voltage controlled oscillator 37). The unijunction transistor oscillator 37 also includes a unijunction transistor 199 having an emitter 201, a base-one 203 and a base-two 205. Base-two 205 is connected to the negative potential on line 175 through a resistor 207, while base-one 203 is connected to ground through a resistor 209.

A transistor 211 has its emitter-collector junction connected in parallel with'the series arrangement of resistors 207 and 209 and the base circuit of unijunction transistor 199. Base 213 of transistor 211 is connected to base 193 of transistor 1 89. A series arrangement comprising a fixed resistor 215, a pair of diodes 217 and 219, a fixed resistor 221 and a variable resistor 223 are connected between the positive DC voltage on line 57 and the negative DC voltage on line 175. A terminal 225 between diode 219 and fixed resistor 221 is connected to base 193 of transistor 189 and base 213 of transistor 211. This series arrangement controls the rate of conduction of transistors 189 and 211 by varying the biasing potential at terminal 225. Thus, the variable resistor 223 may be utilized to provide a rough tuning for the high C end of the musical scale.

During operation of the unijunction transistor oscillator 37, capacitor 197 will be charged through transistor 189 and resistor 191 until the breakdown potential for the unijunction transistor is reached. At this point, capacitor 197 discharges through emitter 201 and base-two 205 of unijunction transistor 199 to provide an output pulse across resistor 207. After discharge of capacitor 197, unijunction transistor 199 is returned to a non-conducting state and capacitor 197 recharges. The charging rate for capacitor 197, and hence the frequency of oscillation of the unijunction transistor oscillator 37, is controlled by the magnitude of resistor 191 and the conducting state of transistor 189.

While the voltage controlled oscillator 37 has been described in terms of a unijunction transistor oscillator, it should be recognized that any voltage controlled oscillator would also be appropriate.

The output of the unijunction transistor oscillator 37 is taken from base-two 205 and connected through a line 227 and capacitor 229 to the base 231 of a transistor 233. Base 231 of transistor 233 is also connected to ground through a resistor 235. Transistor 233 has an emitter 237 which is connected to ground, and a collector 239 which is connected to line 55 through resistor 241. Transistor 233 amplifies the output of the unijunction transistor oscillator 37. This amplified signal is then connected to a first flip-flop circuit 39 by a line 243 connected to collector 239 of transistor 233. Flip-flop circuit 39 comprises a pair of transistors 245 and 247. Transistor 245 has an emitter 249, a base 251 and a collector 253, while transistor 247 has an emitter 255, a base 257 and a collector 259. The circuit connections for transistors 245 and 247 are all illustrated with respect to a terminal board 261.

Terminal board 261, and the circuit connections for the transistors in flip-flop circuit 39 are more fully illustrated in FIG. 5. Terminals A and B of circuit 261 are connected to a resistor 263 and a capacitor 265, respectively. The other sides of resistors 263 and capacitor 265 are connected to a line 267. Resistors 269 and 271 are connected between line 267 and terminals C and G, respectively. A parallel arrangement of a capacitor 273 and a resistor 275 is connected between terminals C and D, while a similar parallel arrangement of a capacitor 277 and a resistor 279 is connected between terminals G and F. A resistor 279 is connected between terminals D and E, and a resistor 281 is connected between terminals E and F. A capacitor 283 is connected between terminals D and F to form a parallel circuit with resistors 279 and 281. Besides the internal arrangement of circuit 261, FIG. 5 also illustrates the external connections of terminals AG to the flip-flop transistors 245 and 247. Terminal C is connected to the collector 253 of transistor 245, while collector 259 of transistor 247 is connected to terminal G. Terminal D is connected to base 257 of transistor 247, and terminal F is connected to base 251 of transistor 245. Terminal E is connected to emitters 249 and 255 and to ground. The external connections of terminals A and B are illustrated in FIG. 3. Terminal A is connected to the positive potential on line 55, while terminal B is provided with the output signal of transistor 233 on line 243.

The operation of flip-flop 39 may now be described. When the circuit is initially energized, one or the other of the transistors 245 and 247 will begin to conduct. Which of the transistors is put into a conducting state would depend upon the particular circuit imbalances that exist. For purposes of this description, it will be assumed that transistor 247 initially is placed in a conducting state. When transistor 247 is conducting, terminal G is essentially at ground potential, and terminal C is at a relatively high potential, but less than the potential at terminal A due to the potential drops across resistors 263 and 269, resulting from the current flow through resistor 263 and the parallel paths comprising resistor 271 and transistor 247, and resistor 269, resistor 275 and resistor 279 to ground. With these circuit conditions, terminal D, which is connected to base 257 of transistor 247, rises toward a potential of half that appearing on terminal C, but limited to the potential drop across the base-emitter diode junction of transistor 247. On the other hand, terminal F, which is connected to the base 251 of transistor 245, is essentially at ground potential, so that transistor 245 remains in a non-conducting state.

Upon the application of a negative going pulse to terminal B from the collector 239 of transistor 233, the conducting state of transistors 245 and 247 will be reversed. During the conduction of transistor 247, capacitor 273 is charged to approximately one-half the potential appearing on terminal C, with the polarity shown in FIG. 5. When the negative pulse is applied to terminal B, capacitor 273 will discharge with a current path from ground through resistor 279, capacitor 273, and resistor 269 to capacitor 265. This direction of current flow will cause a negative pulse to be formed at terminal D and thus transmitted to base 257 of transistor 247. This negative pulse will back-bias the emitter-base junction of transistor 247 and cause transistor 247 to assume a non-conducting state. During the time that transistor 247 is shutting off, the initial rush of charging current gives capacitor 265 a charge with the polarity shown, so that the potential on terminal A is no longer shorted across capacitor 265, as it was upon initial application of the negative going pulse. Thus, there is a potential drop across resistor 281, due to the current flow therethrough, and terminal F is at some voltage value above ground potential. This potential is enough to forward bias the emitter-base junction of transistor 245. Also, the discharge of capacitor 273 through resistor 269 raises the voltage at terminal C above the potential on line 267, so that the collector-base junction of transistor 245 is also forward biased. With both of these junctions forward biased, transistor 245 will begin to conduct current. As the current flow through transistor 245 increases, the potential drop across resistor 269 also increases, so that the potential of line 267 is increased, and the voltage appearing at terminal F is increased. This increased po tential at terminal F will continue to drive transistor 245 into a higher conducting state until transistor 245 reaches a saturated conducting condition. At the same time, terminal C is brought essentially to ground poten- "tial, and thus terminal D is maintained at ground potential to ground potential, the resulting negative going pulse is connected to terminal B of a circuit 285 through a line 287. Circuit 285 is associated with a second flip-flop "circuit 41 and is identical to the circuit 261. Flip-flop circuit 41 is identical to flip-flop circuit 39 and comprises transistors 289 and 291. Transistor 291 has a collector 293 connected to terminal G in the circuit 285. An output signal is taken from collector 259' of transistor 247 through a diode 295, and a second output is taken from collector 293 oftransistor 291 through a diode 297. Since flip-flop circuit 39 produces an output for every two pulses that it receives from the unijunction transistor oscillator 37, the frequency of the output signals through imposed thereon appearing at terminal 22 is also passed along asecond path 141. The DC component of the composite signal is essentially blocked by the coupling capacitor 29. The AC signal is then passed to an AC amplifier comprising a transistor 301 which has an emitter 303, a base 305, and a collector 307. Emitter 303 is connected to ground through a resistor 309, and collector 307 is connected to the positive potential on line 55 through resistors 311 and 313. A bias resistor 315 is connected from collector 307 to base 305 of transistor 301. The AC signal passing through coupling capacitor 29 is applied to base 305 of transistor 301 and an amplified AC signal is taken from collector 307 of transistor 301.

The amplified AC signal on collector 307 is passed through a coupling capacitor 317 to a peak detection circuit comprising a diode 319. Diode 319 serves to clip the peaks of all positive portions of the AC signal passing through coupling capacitor 317 that exceed the magnitude of the potential appearing at a terminal 321. A capacitor 323 is utilized to aid in maintaining the potential at terminal 321 at the desired value. The AC signal with positive peaks clipped by the diode 319 is connected to the'base 325 of a transistor 327. Base 325 is provided with a bias potential from terminal 321 through a resistor 329. An emitter 331 of transistor 327 is connected to terminal 321, while a collector 333 is connected to ground through a resistor 335 and a capacitor 337. When the AC signal appearing on base 325 of transistor 327 is negative relative to the potential at emitter 331, transistor 327 will be biasedto a conducting state and capacitor 337 will be charged through the relatively small resistor 313. When the AC signal appearing on base 325 is positive relative to the potential at emitter 331, transistor 327 will be shut off and capacitor 337 will tend to discharge through resistor 335. The RC time constant of resistor 335 and capacitor 337 is large enough that there will be relatively little discharge of capacitor 337 during the time that transistor 327 is cut off. In other words, the time constant of this RC network is large compared to the period of the AC signal. Thus, capacitor 337 will be constantly charged to essentially the positive value determined by the clipping action of diode 319. Thus, a DC reference voltage of a given magnitude will be present on collector 333 of transistor 327 during the time that an AC signal appears at terminal 22. This DC reference 12 voltage is then connected by a line 339 to succeeding portions of the circuit.

The voltage appearing on line' 339 is also connected to a terminal 341. Terminal 341 connects the voltage, which is in the form of a given magnitude pulse corresponding to the closing of a switch S1 to S13,'to the rhythm trigger circuit 51 shown in FIG. 1. As previously explained, the rhythm trigger circuit coordinates the rhythm of a side man or rhythm accompaniment to the rhythm at which the organ isbeing played.

The signal on line 339 is also passed through a d1ode 343 and a resistor 345 to a base 347 of a transi'stor349. A collector 351 of transistor 349 is connected 'to the positive potential on line 55. Base 347 of transistor'349 is connected to ground through a parallel arrangement of a resistor 353 and a capacitor 355. An emitter 357 of transistor 349 is connected to a midpoint of a pair of resistors 359 and 361. Resistors 359 and 361 are connected in series between the anodes of the output diodes 295 and 297. A series connection of resistors 363 and365 is connected in parallel with the series connection .of resistors 359 and 361 and is grounded at a midpoint between resistors 363 and 365.

The operation of transistor 349 and the attendant circuitry is such that a keying operation is performed for the output diodes 295 and 297. Thus, when a DC reference signal is impressed on line 339 transistor 349 conducts and causes a positive voltage to be applied to the anodes of diodes 295 and 297 through resistors 359 and 361 respectively. This biases diodes 295 and 297 in the forward direction so that any negative signal appearing on collectors 259 and 293 of transistors 247 and 291, respectively, will be transferred to outputs 45 and 47 through capacitors 369 and 371, respectively.

The duration of time for which diodes 295 and 297 are biased for conduction is determined by a sustain circuit 49 (FIG. 1) which is connected to the circuit through resistor 373. Sustain circuit 49 is basically an arrangement for switching various values of resistance into the circuit to control the discharge of capacitor 355. If sustain circuit 49 is completely switched out of the circuit capacitor 355 discharges through resistor 353, which is relatively quate large, and thus transistor 349 is held in a conducting state for a long period of time, and diodes'295 and 297 are biased for conduction for a correspondingly long period of time. This is generally referred to as a long sustain. On the other hand, if sustain circuit 49 is actuated to connect relatively small resistance values from terminal-375 to ground, the capacitor 355 will discharge through the relatively small resistors 345, 373 and those introduced by sustain circuit 49 to provide intermediate durations of sustain.

With this understanding of the circuit features, the overall operation of this arrangement becomes readily apparent. When one of the switches 8-1 to 8-13 is closed by a player choosing a particular organ note the discrete DC voltage corresponding to that switch, along with the constant magnitude AC signal superimposed thereon appears at terminal 22. The signal appearing at terminal 22 is passed by line 139 to detection circuit 23, wherein the superimposed AC signal is removed and capacitor 31 is charged to the discrete DC voltage chosen by'closing of a selected switch. The voltage appearing across capacitor 31 causes capacitor ,185 to be charged to the same value, While the unity gain amplifier 33 isolates capacitor 31 and prevents the charge thereon from being dissipated. The

.voltage on capacitor 185, which corresponds to the chosen discrete DC voltage, controls the charging and discharging of unijunction transistor 199 so that anaudio signal representative of a chosen note is generated. The audio signal is then passed to flip-flop circuits 39 and 41 which produce output audio signals having one-half and one-quarter the frequency of the signal produced by unijunction transistor 199. v

The signal appearing at terminal 22 is also connected to conversioncircuit 27 comprising the AC amplifier transistor 301, peak detector diode 319, and the DC amplifier transistor 327. The resultant DC reference signal appearing across capacitor 337 controls the conduction of transistor 349, which biases output diodes 295 and 297 for conduction during the period that capacitor 355 is charged sufficiently high to maintain conduction of transistor 349'. During the time that output diodes 295 and 297 are biased for conduction output signals from the flip-flop circuits 39 and 41 are present on output terminals 45 and 47, which correspond to the eight foot and sixteen foot bus bars of the organ. The duration of time for which diodes 295 and 297 are forward biased depends upon the length of time that the chosen switch is maintained closed and the discharge time of capacitor 355. The discharge time of capacitor 355 is controlled by a standard sustain circuit 49.

Up to this point, the discussion has related to an electronic organ having a single octave range, or one having frequency dividers connected in series to produce multiple octave tones. A one octave range is, of course, not con1- pletely satisfactory in many environments, and series frequency dividers tend to reduce the tone quality and volume. Thus, it would be desirable to provide, in some instances, at least two and perhaps more octaves of electronic organ notes without using series connected frequency dividers. One way to do this would be to provide additional discrete voltages and additional switches to control the variable frequency tone oscillator. However, such an arrangement has the disadvantage of requiring a much greater range of frequencies from the voltage controlled oscillator. This results in less stability of the oscillator produced frequencies. Further, such a range of frequencies means that there must be a more precise relationship between discrete control voltages and the corresponding frequencies, i.e., a greater degree of frequency resolution. Thus, it is preferable to use an oscillator having a single octave range of frequencies and to achieve the desired multiple octave range by providing a single frequency division of the oscillator output signal. It is necessary, of course, to provide for appropriate regulation of the single frequency divider to obtain the desired factor of frequency division.

Such an arrangement utilizing single-pole switches is disclosed in FIG. 6. In this arrangement, the circuit is the same as that disclosed in FIG. 1 except that a single flip-flop octave divider has been utilized instead of separate flip-flop circuits. With this arrangement, a single output tone signal having the proper octave relationship is produced. To aid in the description of this embodiment, components identical to those described in relation to the FIG. 1 embodiment have been similarly numbered with primed numbers.

From FIG. 6 it may be seen that an additional set of high octave switches SA-1 to SA-12 has been added. These switches are identical to switches S-1 to 8-13 and have been arranged in a similar ladder network. The ladder network of the switches SA-l to SA*12 is connected in series with the ladder network of switches S-1 to 8-13. Thus, a note played in the high octave designated by switches 8-1 to 8-13 will pre-empt the playing of a note corresponding to a switch in the low octave switches designated SA-l to SA-12. The 'basic operation of the tone selection feature of the circuit is not altered by the addition of the low octave switches.

However, the actuation of a switch in the group of switches SA-l to SA-IZ not'only produces a signal at terminal 22' but also passes the signal through a coupling capacitor 377 to a second conversion circuit 379. Conversion circuit 37 9 is identical to conversion circuit 27 and will not be desribed in detail here. The output pulse produced by conversion circuit 379 (which could have a negative value rather than the positive output across capacitor 337 by appropriate adjustment of the circuit parameters) is connected to an octave control flip-flop circuit 14 381. A reset capacitor 383 is connected from the output 385 of conversion circuit 27' to flip-flop 381.

Flip-flop 381 has two conditions, an off state in which no output signal is produced and an on" state when an output signal is produced. Upon selection of any tone, flip-flop 381 is placed in the off state by the leading edge of the signal from output 385 of conversion circuit 27', through capacitor 383. When a switch SA-l to SA-12 is actuated the conversion circuit 379 is activated and fiip flop 381 is placed in the on state, after the signal from conversion circuit 27' has initially reset it to the off state.

The output of the octave control flip-flop 381 is then connected to an octave divider flip-flop 391. Octave divider flip-flop 391 is essentially the same as flip-flop 39 in the first embodiment and performs an identical frequency dividing function when a switch in a group of switches 5-1 to 8-13 is actuated. However, when a switch in the group of switches SA-l to SA-12 is actuated, the signal from the octave control flip-flop 381 is applied to the octave divider flip-flop 391 to decrease the frequency of the signals produced by the flip-flop 391 by another factor of two. Thus, when a switch 8-1 to 5-13 is actuated, the output of flip-flop circuit 391 is one half the frequency produced by the voltage controlled oscillator 37. However, if a switch SA-l to SA- 12 is actuated, the signal from the octave control flipfiop 381 causes the flip-flop 391 to produce output pulses at one-fourth the frequency of the signal from the voltage controlled oscillator 37'. In this manner, the audio signal appearing at the output 393 of flip-flop circuit 391 (which is then conveyed to appropriate footage dividers) has the 1 appropriate octave frequency, but the oscillator 37' only needs a frequency range of one octave. Further, the decrease in tone quality resulting from multiple series frequency divisions is obviated.

It should be understood that the embodiments described are merely exemplary of the preferred practices of the present invention and that various changes, modifications, and variations may be made in the details of construction, arrangements, and operations of the elements disclosed herein, without departing from the spirit and scope of the present invention, as defined in the appended olaims. i

What is claimed is:

'1. A voltage selection arrangement comprising:

DC source means adapted to provide a plurality of discrete DC voltages;

AC supply means adapted to provide an AC signal for superimposition on each of the discrete DC voltages;

detection means for removing the superimposed AC signal from individual ones of the discrete DC voltages as the discrete DC voltages are selectively conveyed thereto;

switch means for selectively conveying the discrete DC voltages to the detection means; and

voltage responsive means connected to the detection means and adapted to be operated thereby,

whereby the discrete DC voltages are selectively applied to the voltage responsive means through the switch means and the detection means in order to effect operation of the voltage responsive means.

2. An arrangement as claimed in claim 1 wherein the DC source means comprises:

a constant value DC voltage source; and

a voltage divider network comprising a series of resistive elements with tap points placed between the resistive elements, the voltage divider network being connected across the DC voltage source and the AC supply means adapted to provide an identical AC signal for each end of the voltage divider network.

3. A device as claimed in claim 1 wherein the switch means comprises a plurality of single-pole switches each connected to a point in :the DC source means corresponding to a given 'one of the discrete DC Voltages.

4. An arrangement as claimed in, claim 1 wherein the detection means comprises:' I

La first pair of unilateral conducting devices connected in series and biased for conduction;

a second pair of series-connected unilateral conducting devices connected in parallel with the first pair of unilateral conducting'devices and biased for nonconduction; I- 9 I i input means conveying the discrete DC voltages with the AC signal superimposed thereon to a common juncture point of the first pair of unilateral conducting devices; and i I output means connected to a common juncture point of the second pair of unilateral conducting devices and conveying the discrete DC voltages to the voltage responsive circuit. 4 5. An arrangement as claimed in claim 4 and further comprising a storage capacitor connected to the common juncture point of the second pair of unilateral conducting devices.

6. An arrangement as claimed in claim 4 wherein the output means comprises a unit gain amplifier.

7. An arrangement as claimed in claim 1 and further comprising:

conversion means connected to the switch means and responsive to the AC signal superimposed on the discrete DC voltages to produce a DC reference signal of a given amplitude; and reference signal responsive means connected to the conversion means and controlled thereby, whereby actuation of the switch means causes the AC signal superimposed on the discrete DC voltages to be applied to the conversion means to control the reference signal responsive means. I 8. An arrangement as claimed in claim 7 wherein the conversion means comprises:

an AC peak detector circuit for limiting the amplitude of the AC signal at a given level; and

i I a DC amplifier responsive to the AC signal up to'the given level to charge a storage circuit and thereby to produce the DC reference signal.

9. A voltage selection arrangement comprising:

DC source means adapted to provide a plurality of discrete DC voltages;

AC supply means adapted to provide an AC signal for superimposition on each of the discrete DC voltages;

first switch means for selectively conveying individual ones of the discrete. DC voltages to a switch means output terminal; 6

' detection means connected to the. switch means output terminal for removing the superimposed AC signal from individual ones of the discrete DC voltages as the discrete DC voltages are selectively conveyed thereto;

a voltage responsive variable frequency signal generator connected to the detection means and adapted to be controlled thereby; I

first conversion means connected to. the switch means output terminal and responsive to the AC signal superimposed on the discrete DC voltages to pro- 'duce a first DC reference signal of a given amplitude; and

first reference signal. responsive means connected to the first conversion means and controlled thereby said reference signal responsive means adapted to 16 regulate the output of the variable frequency signal generator, I I f whereby regulation of the output of the variable frequency signal generator is directly relatedto control of the frequency of the signal generator.

10. An arrangement as claimed in claim 9f and further comprising: v II second switch means for selectively conveying individual ones of the discrete DC yoltages to the switch means output terminal; I I Y second conversion meansconnected to the second switch means and responsive to .the AC signal super.- imposed on the discrete DC voltages't'o produce a second DC reference signal of a given amplitude;

and

second reference signal responsive means connected to the second conversion means and controlled thereby; said second reference signal responsive means adapted to further regulate the output of the variable frequency signal generator.

11. An arrangement as claimed in claim 9" wherein:

the voltage responsive means comprises a variable frequency oscillator functioning as a tone generator for a musical instrument; f

- the first switch means are adapted for manual actuation during the course of play of the musical instru- Inent; and

the first reference signal responsive means is a keying circuit for the musical instrument.

12. An arrangement as claimed in claim 11 wherein the first switch means comprises a plurality of single-pole double-throw switches each connected to a point in the source means corresponding to a givenone of the discrete DC voltages, the switches normally beingconnected in a closed series circuit with actuation of any of the switches opening the series circuit at that point. p

13. An arrangement as claimed in claim 12 and further comprising:

a second plurality of single-pole double-throw switches normally connected in series with the first plurality of switches;

a second conversion means connected to the juncture of the first plurality of switches and the second plurality of switches to produce a second DC reference signal of a given amplitude; and

a second reference signal responsive means connected to the. second conversion means and controlled there by to effect multiple octave 'tone regulation of the output of the tone generator.

References Cited HERMAN KARL SAA LBACI- I, Primary Examiner L. ALLAHUT, Assistant Examiner 1 I US. Cl. X.R. 

